netdev - Re: [PATCH] mlx4_en: add UFO support

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Message-ID: <20120803135419.GB5736@oc1711230544.ibm.com>
Date:	Fri, 3 Aug 2012 10:54:19 -0300
From:	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
To:	Yevgeny Petrilin <yevgenyp@...lanox.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Or Gerlitz <ogerlitz@...lanox.com>
Subject: Re: [PATCH] mlx4_en: add UFO support

On Fri, Aug 03, 2012 at 08:29:26AM +0000, Yevgeny Petrilin wrote:
> > 
> > Mellanox Ethernet adapters support Large Segmentation Offload for UDP
> > packets. The only change needed is using the proper header size when the
> > packet is UDP instead of TCP.
> > 
> > This significantly increases performance for large UDP packets on platforms
> > which have an expensive dma_map call, like pseries.
> > 
> > On a simple test with 64000 payload size, throughput has increased from
> > about 6Gbps to 9.5Gbps, while CPU use dropped from about 600% to about
> > 80% or less, on a 8-core Power7 machine.
> > 
> Hi Thadeu,
> Can you please send the info regarding the adapter you are testing with? What test are you running?
> I just tried this patch with netperf on my x86_64, and it doesn't work. Packets are not fragmented properly (fragment offsets are not calculated).
> It is true that the TX side doesn't work as hard (OS doesn't need to do the fragmentation), but traffic is not sent properly on the wire.
> 
> I'll do further investigation and get back with more details.
> 
> Yevgeny
> 

Hi, Yevgeny.

You are right. After generating a dump on the receiving end, and sending
a single large packet, I did notice that fragment offsets were all 0,
more fragments flag is not set and id is incremented.

Does the hardware really support UFO as documented? Should we just write
the IP header to the descriptor? I will try this and report my results.
Meanwhile, can you find out what is needed to get this working?

Thanks a lot.
Cascardo.

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